The present invention relates to expansible dry seal gasholders of the vertical-lift piston type and, in particular, to such gasholders in sizes of 100,000 cubic feet capacity and larger.
Such a gasholder is disclosed in U.S. Pat. No. 2,606,824, issued to J. W. Allen on Oct. 12, 1952, which gasholder comprises an outer container in which is disposed a vertically movable piston and an annular fender or backstop structure disposed between the piston and the container side wall and spaced therefrom, with flexible sealing means connecting the fender structure to the side wall and the piston for closing the spaces therebetween and permitting vertical movement of the fender structure and piston with respect to each other and with respect to the side wall, whereby the piston and fender structure cooperate with the side wall to define an expansible gas storage chamber therebeneath. In the Allen apparatus the piston rises into engagement with the fender structure, so that further lifting of the piston also lifts the fender structure. The piston cannot rise above the fender structure, so that the maximum volume of the storage chamber is determined by the distance that the fender structure can be lifted, which is in turn determined by the length of the sealing means interconnecting the fender structure and the container side wall.
Another version of this type of expansible gasholder is disclosed in U.S. Pat. No. 3,436,196, issued to J. H. Wiggins on Apr. 1, 1969. Wiggins provides hook lift structures and cable linkages between the piston and the fender structures, which arrangement permits the piston to rise above the fender structure.
But in both Wiggins and Allen, when the piston is at a level of maximum slack in the sealing member which connects it to the fender structure, the piston can undergo considerable lateral movement, which may cause one side of the piston to ride up inside the hook or compression member of the fender structure and not properly engage it, which could result in jamming of the piston against the fender structure. Furthermore, in both of these prior art structures, the piston and the fender structure are capable of considerable rotational movement which can place severe stresses on the flexible sealing members therebetween. These difficulties may be particularly aggravated in the case of gasholders with high rates of gas input and discharge, such as in the gas storage systems utilized in the steel industry.